A cellular radiotelephone communications system consists of multiple cells covering a geographical area, a metropolitan area for example, each cell consisting of an antenna coupled to a low power transceiver. Each cell has a number of frequencies assigned to it, the frequencies divided into control channels, paging channels, and voice channels. The paging and control channels are used for reciprocal identification between the radiotelephone and the system. The location of the control channels in the cell's frequency spectrum identifies the type of cellular system, A or B (see Electronic Industries Association 553). A metropolitan area typically has one of each type of system.
A cellular radiotelephone operating in a cellular radiotelephone system must identify itself to the system servicing the radiotelephone, allowing the system to interface the radiotelephone to the landline telephone system. The identification typically informs the system that the radiotelephone is active in that particular system in addition to telling the system the telephone number assigned to the radiotelephone. The system informs the radiotelephone of its unique identification code. This identification process, taking place over a paging channel, is accomplished when the radiotelephone is powered up and receiving but not transmitting, in other words, in an idle state.
Autonomous registration is such an identification method (U.S. Pat. No. 4,775,999 to Williams, assigned to Motorola, describes such a registration method). This registration is performed at various time intervals to indicate that the radiotelephone is active in the system. If the radiotelephone moves to another cellular communications system it must register in the new system.
In order for a radiotelephone to register in its home system, it must contain a telephone number assigned to the particular system identification code for that system. If the radiotelephone does not have a number for that system it will still be able to operate in that system but will be considered a roaming radiotelephone and, therefore, typically pay higher rates for using the system.
One solution to this problem has been making radiotelephones with the capability of containing multiple telephone numbers assigned to multiple corresponding system identification codes. If the radiotelephone moves to another system for which the radiotelephone has a telephone number, the user can switch the radiotelephone to that number, thereby paying lower rates. This creates a problem, however, when the radiotelephone has a large number of telephone numbers from which the user can choose. When the radiotelephone travels to another system, the user has to remember the specific telephone number assigned to that particular system. There is a resulting need for a process for informing the radiotelephone user in which system the radiotelephone is located and the telephone number assigned to that system.